Operation With Two Plcs; Nc/Plc Interface; I/O Device Assignment With 2 Plcs - Siemens SINUMERIK 880 SW 6 Planning Manual

01.93
1.5

Operation with two PLCs

1.5.1

NC/PLC interface

When operating with two PLCs, the user must determine whether the NC/PLC interface is to
be processed by PLC I or PLC II. This is specified by machine data. The choice can be made
channel, axis- and spindle-specific, that is to say each NC channel, axis and spindle is
assigned to one of the PLCs.
If a SIMATIC S5-155U is used, it is not possible to use two PLCs.
1.5.2

I/O device assignment with 2 PLCs

I/O submodules at the operator panel
The inputs and outputs that are connected to the operator panel by means of I/O submodules
are available to both PLCs. Here again, PLC machine data are used to specify which PLC
processes an I/O submodule; outputs can be switched only by one PLC in each case.
Central I/O devices declared global
The SINUMERIK I/O modules do not have a link bus interface. Signals connected in the centr-
al controller can therefore be read and switched only by the PLC whose local bus accommo-
dates the I/O module to which the signals are connected.
If, when operating two PLCs, PLC II is to process signals connected to the local bus of PLC I,
PLC I must make these signals available to PLC II. The signal flow for this example is shown in
the following figure.
Transfer of input signals to PLC II
PLC I periodically reads the inputs of the I/O module (in a 10 ms cycle) and transfers the sign-
als to an internal interface in the link RAM. PLC II obtains this internal input image at the start
of the cycle and transfers it to its PII where the user program can read the status of the inputs.
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c) up to and including software version 6
© Siemens AG 1991 All Rights Reserved
SINUMERIK 880 (PJ)
c)
c)
6ZB5 410-0HE02
1 General Overview
1.5 Operation with two PLCs
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